209
23
Pediatric Movement Disorders
HUNTINGTON’SDISEASE 209 SYDENHAM’SCHOREA 210
DYSTONIAMUSCULORUMDEFORMANS 212 TICDISORDERS 213
Huntington’s Disease
Vignette
An 8-year-old girl became irritable, apathetic, dis- tractible, and lost interest in her schoolwork and dance classes. She was noted to have sudden jerk- ing movements in her arms and started experienc- ing generalized tonic-clonic seizures. A year later she was more withdrawn, not following questions or commands, sometimes remaining in a catatonic posture. On examination, there was rigidity with loss of facial expression. Her prior developmental history was unremarkable. She had no siblings. Her father had involuntary movements and grimacing and was demented.
Summary An 8-year-old girl with progressive cognitive impairment associated with seizures and parkinsonian features (rigidity, loss of facial expression). In the family history, her father has dementia, facial grimacing, and involuntary movements.
Localization and Differential Diagnosis
The vignette describes an extrapyramidal disorder that occurs during childhood and is associated with progres- sive dementia and seizures.
The family history with a father affected by dementia and involuntary movements suggests a hereditary domi- nant disorder. Among the hereditary, predominantly ex- trapyramidal, syndromes occurring during late child- hood and adolescence the following should be considered first:
• Childhood and juvenile forms of Huntington’s disease.
• Wilson’s disease.
• Hallervorden-Spatz disease.
Huntington’s disease is a progressive degenerative dis- order with an autosomal dominant pattern of transmis- sion. The clinical manifestations in children are domi- nated by cognitive and behavior abnormalities, rigidity, loss of facial expression, decreased voluntary move- ments, and seizures. In the majority of childhood-onset cases there is an affected father.
Wilson’s disease, which always needs to be ruled out in a child presenting with signs of extrapyramidal system dysfunction is an autosomal recessive disorder character- ized by the accumulation of copper in the liver, basal ganglia, and cornea. Younger children usually present with signs and symptoms of significant liver dysfunction rather than neurological involvement. Neurological man- ifestations, with only minimal symptoms of liver disease, are more likely when the onset of symptoms is in the second decade (Fenichel). Speech abnormalities with dysarthria as well as tremor dystonia and gait distur- bances are often the presenting neurological symptoms.
Emotional lability and psychosis can also be the initial feature, but seizures and marked dementia are not usually a significant characteristic of the disease except in few cases.
Hallervorden-Spatz disease is a familial disorder that manifests with signs of involvement of the extrapyrami- dal system such as rigidity, dysarthria, choreoathetosis, and gait dysfunction, in association with signs of pyra- midal involvement such as spasticity and hyperreflexia.
Behavioral abnormalities and cognitive impairment can occur and visual abnormalities such as retinitis pigmen- tosa and optic atrophy can also be present. Seizures are not common. Typical pathological findings include hy- perpigmentation of the pallidum and substantia nigra.
Other extrapyramidal disorders such as idiopathic tor- sion dystonia, familial calcification of the basal ganglia, juvenile paralysis agitans, chorea-acantocytosis, and so on are easily differentiated by their clinical features.
210 23. Pediatric Movement Disorders
Considering the information presented in the vignette, Huntington’s disease is the preferred diagnosis.
Clinical Features
Huntington’s disease (HD) in the pediatric population usually presents in the first decade of life (between 5 and 12 years of age) with symptoms characterized by behav- ioral and cognitive deterioration, rigidity, dystonia, and seizures.
Seizures, which are usually not observed in adult pa- tients with HD, can be a prominent initial manifestation and may affect about 50 percent of children with HD (Menkes). Epileptic seizures can be represented by tonic- clonic convulsions, absence, and myoclonic seizures.
Tonic-clonic or myoclonic status can also occur.
Rigidity causing gait disturbances is common, and dystonia, loss of facial expression and associated move- ments, and decreased voluntary movements are signifi- cant features in the majority of pediatric patients. Cho- reoathetosis and hyperkinesia are not common in the pediatric age group with HD.
Mental deterioration with progressive dementia is an important characteristic feature. Behavior abnormalities manifest with irritability, distractibility, emotional labil- ity, negativism, and even catatonia. Most of childhood- onset cases have inherited the gene from an affected fa- ther. The HD gene has been localized to the short arm of chromosome 4 and contains an abnormal repeat of the trinucleotide CAG (cytidine-adenine-guanidine).
Diagnosis
The diagnosis is based on the clinical features and family history. Neuroimaging studies demonstrate caudate atro- phy and PET studies reveal significant reduction in cau- date glucose metabolism. DNA analysis detects the ab- normal gene.
Treatment
The treatment is symptomatic and is based on the use of anti-parkinsonian medications to control rigidity and dys- tonia. Behavioral abnormalities may respond to neurolep- tics. The use of baclofen (GABA agonist) and diltiazem (calcium-channel blocker that might block the action of glutamate on calcium channels) is controversial.
Sydenham’s Chorea
Vignette
A 10-year-old Mexican immigrant was reported by her teacher as being restless, inattentive, over-
emotional, and fidgety. Irregular jerking move- ments of her distal upper extremities and face were noted, and she seemed particularly troubled when eating, drinking from a cup, or writing. Her family and developmental histories were normal. Six months earlier, while still in Mexico, she had ex- perienced knee pain and swelling accompanied with fever. Her family reported no other medical history.
Summary A 10-year-old girl with onset of involuntary movements and prior history of knee pain, swelling, and fever.
Localization and Differential Diagnosis
The involuntary, irregular jerking movements that inter- fere with activities such as writing or feeding in this pa- tient, plus the fidgety, restless, and overemotional behav- ior observed by her teacher most likely are indications of a choreic disorder. Childhood chorea can be attributed to various etiologies:
• Infectious disorders, such as Sydenham’s chorea, diph- theria, viral encephalitis, and so on.
• Immunological disorders, such as systemic lupus ery- thematosus, periarteritis nodosa, and sarcoidosis.
• Drug-induced causes, such as related to the use of neu- roleptics, anticonvulsants, and so on.
• Toxic causes, such as due to manganese, carbon mon- oxide, toluene, and alcohol.
• Metabolic and endocrine disorders, such as hypogly- cemia, hyperglycemia, hypocalcemia, hyperthyroid- ism, and Addison’s disease.
• Structural disorders, such as tumors and arteriovenous malformations.
• Bilateral cerebral dysfunction, such as postanoxia.
• Genetic and hereditary degenerative disorders, such as childood Huntington’s disease, Hallervorden-Spatz disease, Lesch-Nyhan syndrome, and so on.
Sydenham’s chorea (St. Vitus’ dance) is a well-known choreic sequelae of infection with group A streptococcus.
It affects children between 5 and 15 years of age, par- ticularly females. A beta-hemolitic streptococcal infec- tion of the pharynx may occur 1 to 7 months prior to the onset of the neurological manifestations in most patients.
The movements are typically choreoathetoid and prefer- entially involve the face and upper extremities, unilater- ally or bilaterally. Sydenham’s chorea, polyarthritis, and carditis are important features of rheumatic fever, the re- sult of an antecedent group A streptococcal pharyngeal infection. A prior history of pharyngitis is not always given by the patient and families. The duration of the chorea varies from three months to two years.
Other infectious processes that can be responsible for
the occurrence of chorea include bacterial, such as sub- acute bacterial endocarditis, neurosyphilis, diphtheria, tu- berculosis, Lyme disease, and viral infections, such as viral encephalitis, mononucleosis, HIV, Epstein-Barr, varicella, pertussis, and so on.
Immunological causes of chorea include, in particular, systemic lupus erythematosus, Behc¸et’s disease, Schonlein-Henoch purpura, antiphospholipid antibodies syndrome, and so on. Systemic lupus erythematosus in children can manifest with psychosis, seizures, cranial neuropathy, and rarely with chorea as the only presenta- tion. The presence of systemic symptoms such as fever, rash, lymphadenopathy, hematuria, albuminuria, and so on, and laboratory studies, particularly antibodies against DNA, help confirm the diagnosis.
Drug-induced causes are now considered the most common cause of chorea in children (Robertson et al.).
Among the drugs, neuroleptics, anticonvulsants, anti- emetic, noradrenergic stimulants, and so on, can be in- cluded. Tardive dyskinesia indicates a condition associ- ated with the use of neuroleptics and characterized by abnormal involuntary movements such as choreic move- ments involving the face and limbs. Withdrawal emergent syndrome (Robertson et al.) refers to the first appearance of involuntary movements and chorea after interruption of neuroleptic treatment.
Toxic agents that may induce chorea include carbon monoxide, thallium, toluene (glue sniffing), and so on.
Metabolic and endocrine disturbances can also cause sec- ondary chorea. Electrolyte disturbances such as hypo- glycemia, hyperglycemia, hypocalcemia, hypomangane- semia, and hepatic and renal failure can be responsible for secondary chorea. The endocrine disorders primarily include hyperthyroidism, but also hypoparathyroidism, Addison’s disease, and so on. Some vitamin deficiencies such as vitamin B12, beriberi, and pellagra can present with chorea.
Chorea can also be secondary to diffuse cerebral dys- function due to perinatal anoxia or decreased cerebral perfusion due to postcardiopulmonary bypass. Structural cerebral lesions like tumor, arteriovenous malformations or cerebrovascular accidents can also present with chorea.
Trauma has also been involved in some cases.
Hereditary degenerative disorders manifesting with chorea include the following:
• Juvenile Huntington’s disease, as previously described, is an autosomal dominant disorder usually transmitted by the affected father and characterized by progressive cognitive impairment, rigidity, seizures, and choreo- athetosis.
• Wilson’s disease is an autosomal recessive disorder of copper metabolism characterized by hepatic failure and neurological features particularly involving the extra- pyramidal system with tremor, rigidity, dystonia, dys- arthria, choreoathetosis, and so on.
• Hallervorden-Spatz disease is a rare autosomal reces- sive disorder of iron metabolism, manifesting with choreic movements, athetosis, dystonia, rigidity, cog- nitive impairment, retinitis pigmentosa, seizures, and so on.
• Pelizaeus-Merzbacher disease is an X-linked recessive disorder of myelin formation characterized by invol- untary movements with chorea or athetosis, cerebellar ataxia, pendular nystagmus, developmental regression, spasticity, optic atrophy, and so on.
• Fahr’s disease, or familial calcification of the basal ganglia, manifests with choreoathetosis, mental im- pairment, microcephaly, and seizures. There is pro- gressive calcification of the basal ganglia.
• Neuroacanthocytosis is characterized by chorea in as- sociation with seizures, orolingual dystonia, and acan- thocytosis (acanthocytes are abnormal erythrocytes that have thorny projections from the cell surface).
• Ataxia-telangiectasia is a hereditary autosomal reces- sive disorder clinically characterized by progressive ataxia, telangiectasias, and recurrent sinopulmonary in- fections. Choreoathetosis can also be observed, par- ticularly in infants.
• Benign familial hereditary chorea is an autosomal dominant hereditary disorder manifesting with chorea, dysarthria, and normal cognitive function.
• Genetic metabolic disorders such as GM1 and GM2 gangliosidosis, Leigh syndrome, lipofuscinoses, and so on, can also include chorea in their symptomatology.
Hereditary paroxysmal choreas need also to be mentioned:
• Paroxysmal dystonic choreoathetosis is an autosomal dominant hereditary disorder that manifests with epi- sodes of choreic movements and dystonia of various duration from minutes to hours.
• Familial paroxysmal kinesiogenic choreoathetosis is a hereditary disorder characterized by brief, recurrent ep- isodes of unilateral choreoathetosis precipitated by a sudden movement (Robertson).
Clinical Features
Sydenham’s chorea represents a late sequelae of group A streptococcal pharyngitis. The neurological manifesta- tions usually tend to present one to six months after the streptococcal infection. Affected children range from 5 to 15 years of age and are preferentially girls. The disorder manifests insidiously or acutely with involuntary move- ments that involve the face and distal part of the upper extremities. The involuntary movements disappear dur- ing sleep or sedation. The child is first noted to be restless, clumsy, and fidgety. The speech becames dysarthric, and hypotonia may create abnormal postures. The hand grip waxes and wanes when the child is asked to squeeze the
212 23. Pediatric Movement Disorders
examiner’s hand, a phenomenon called “milkmaid sign.”
Seizures rarely occur. Behavioral dysfunction, includes, in particular, tics and obsessive-compulsive disorder.
Diagnosis
MRI of the brain, which is important in order to rule out structural lesions, is usually normal but may show high signal on T2-weighted images in the head of the caudate and in the putamen.
Some laboratory tests should be considered including
• Blood count and differential.
• Blood chemistry.
• Thyroid function tests, erythrocyte sedimentation rate.
• Antinuclear antibodies titer.
• Anticardiolipid antibodies.
• Antistreptolisin O titer.
In selected cases, other laboratory studies include
• Blood smear for acantocytes.
• Ceruloplasmin, serum copper.
• VDRL.
• HIV.
• Heavy metal screen.
• Lysosomal enzymes.
Treatment
Streptococcal infection should be aggressively treated with penicillin. Treatment of chorea is based on the use of dopamine antagonists, benzodiazepines, or valproate.
Neuroleptics with more specific D2receptor antagonism (such as haloperidol) are effective for the more intense chorea, but carry a risk of tardive dyskinesia (O’Brien).
Dystonia Musculorum Deformans
Vignette
A 10-year-old boy started having difficulty walking at the age of 6 because of intermittent abnormal posture of his left foot with plantar flexion and in- version as it approached the ground. The symptoms slowly progressed and, at age 9, the boy was unable to walk because both feet were constantly flexed.
Eventually, involuntary flexion appeared at the left wrist as well as torticollis and facial grimacing. His medical and developmental history were normal.
The patient was the product of a full-term, uncom- plicated pregnancy. A paternal uncle in the family history had difficulty with handwriting. Upon ex- amination the boy had normal intelligence. Cranial nerves, motor strength, reflexes, and sensation were intact.
Summary A 10-year-old boy with involuntary move- ments of his lower extremities consisting of abnormal plantar flexion and inversion of his ankles that progressed from age 6. In addition, left wrist flexion torticollis and facial grimacing are described. Birth and developmental history are normal. Mental status, cranial nerves, motor strength, sensation, and reflexes are normal. In the family history, one uncle has trouble with handwriting.
Localization
The disorder affecting this child may be localized to pa- thology involving the extrapyramidal system. The vi- gnette describes a case of dystonia, which by definition is characterized by sustained muscle contraction of ago- nist and antagonist muscles, frequently causing repetitive abnormal movements and posture.
Diagnosis and Differential Diagnosis
The vignette indicates a normal perinatal and develop- mental history and no past history of exposure to drugs or toxins. The neurological examination shows a child with normal cognitive function and normal strength, sen- sation, and reflexes. This helps in narrowing the diag- nostic possibilities.
A family history consistent with an uncle with “hand- writing problems” points to a hereditary disorder. Torsion dystonia can clearly explain all the symptoms expressed in the vignette. It is a hereditary disorder characterized by involuntary, sustained muscular contractions com- monly involving the foot, with movements of plantar flexion and inversion, which initially occur intermittently and then became constant.
The most important consideration in the differential di- agnosis is Wilson’s disease since it is a treatable condition and needs to be excluded in all patients developing move- ment disorders. In Wilson’s disease, signs of hepatic dys- function may predominate in children. Neurological symptoms include rigidity, tremor, bradykinesia, and dys- arthria in addition to dystonia. Kaiser-Fleisher rings are characteristic and the serum ceruloplasmin is generally decreased.
Hereditary neurodegenerative disorders, such as Hunt- ington’s disease, Hallervorden-Spatz syndrome, Fahr’s disease, ceroid lipofuscinosis, ataxia-telangiectasia, neu- roacanthocytosis, and so on, may manifest with dystonia but usually they are also characterized by other neurolog- ical and multifocal abnormalities, such as mental deteri- oration, seizures, retinitis pigmentosa, and so on.
Symptomatic generalized dystonia may be secondary to a neoplastic or vascular process, trauma, encephalitis, or hypoxic or metabolic encephalopathy. Secondary dys- tonia in children is often caused by perinatal asphyxia (Menkes). Vascular cerebral malformations and neoplas-
tic conditions can present with localized or generalized dystonia that may mimic the idyopathic type.
Dystonia can also be related to an acute brain infection or trauma, or can be secondary to toxic agents such as manganese or carbon monoxide, or drug ingestion such as neuroleptics, phenytoin, phenobarbital, anthistamines, and so on.
Psychogenic dystonia is also a consideration in a small percentage of children but some clinical characteristics such as bizarre movements, gait inconsistency, and de- creased movement when the child is distracted, may help the correct diagnosis.
In summary, dystonia can be etiologically distin- guished into primary, or idiopathic, and secondary, or symptomatic. The idiopathic group is characterized by disorders with dystonic postures as the only abnormality and with absence of other neurological symptomatology.
Symptomatic dystonias, which are associated with hered- itary or acquired disorders, usually present with a multi- tude of symptoms including dementia, seizures, spastic- ity, hyperreflexia, ataxia, retinitis pigmentosa, and so on.
Clinical Features
Idiopathic torsion dystonia is a familial or sporadic dis- order with various modes of inheritance: autosomal dom- inant, autosomal recessive, or X-linked recessive. Gen- eralized dystonia is the most common form observed in children. The age of presentation varies between 6 and 12 years in children who have a normal developmental history.
The first symptoms can present with intermittent in- voluntary posturing of the foot with plantar flexion and inversion while the child walks, but not during rest or when he is running or walking backwards. With progres- sion of the disease, the motor abnormalities became per- sistent and may spread to involve contiguous areas, such as the pelvic girdle muscles, shoulders, and spinal and neck muscles, often interfering with daily activities. Al- most all children for whom the dystonia begins in the legs progress to have generalized dystonia within one to five years (Robertson et al.). Dystonia of the tongue and pharyngeal and laryngeal muscles may cause dysarthria and dysphagia. Paroxysmal dyspnea has also been de- scribed (Menkes). The dystonic movements disappear during sleep and are exacerbated by stress, fatigue, and excitement.
The neurological examination in idiopathic torsion dystonia does not reveal any abnormality except for the dystonic posture and movements. The intellectual func- tion is normal.
Dopa-responsive dystonia, which affects children in the first decade of life, needs to be differentiated from idiopathic torsion dystonia because of its characteristic diurnal fluctuations and excellent response to levodopa treatment.
Myoclonic dystonia is an inherited condition charac- terized by torsion dystonia in association with myoclonic jerks.
Treatment
The treatment of torsion dystonia is based on the use of anticholinergic agents such as trihexyphenidyl (Artane), which is given in a dose that starts at 2 to 4 mg/day and is gradually increased up to 60 to 80 mg/day until the maximum benefit or intolerable side effects are encoun- tered (Menkes). Baclofen has been beneficial in some pa- tients. Intratheral baclofen has been used in selective cases of severe intractable torsion dystonia. Levodopa ap- pears to be effective in patients with late-onset dystonia.
Botulinum toxin can be utilized in the treatment of facial dystonia, but not in the generalized form. In intractable cases, surgery may represent an option, particularly uni- lateral or bilateral pallidotomy.
Tic Disorders
Vignette
An 8-year-old boy was referred to an allergist after the teacher noticed that he was sniffing, coughing, and clearing his throat with unusual frequency. The mother admitted that at home he seemed very ner- vous, often blinking, grimacing, grunting, or shoul- der shrugging, especially while watching televi- sion. These symptoms probably started at age 6. On examination he was a very bright boy, with occasional squeezing of his eyelids and nasal twitches. The neurological examination was unre- markable. Past medical and developmental history were normal.
Summary An 8-year-old boy with history of involuntary movements (motor tics) and involuntary making of sounds (phonic tics) since age 6. The neurological and medical history are normal.
Localization, Differential Diagnosis, and Diagnosis
Tics, characterized by involuntary, sudden, purposeless, repetitive, stereotyped, motor movements or vocaliza- tions, are the most common involuntary movement dis- orders of childhood (Erenberg). Tic disorders vary in se- verity from a transient tic disorder to Tourette’s syndrome (TS). Transient tic disorder, which is common in children, has a duration of less than one year. Chronic tic disorder, characterized by motor or vocal tics but not both, has a duration longer than a year.
214 23. Pediatric Movement Disorders
The boy described in the vignette has experienced both motor and vocal tics for over a year, therefore he strongly represents a case of Tourette’s syndrome. Diagnostic cri- teria for Tourette’s syndrome, according to the DSM-IV- TR, include
• Onset before 18 years of age.
• Presence of multiple motor tics and one or more vocal tics.
• Recurrence of the tics many times a day, nearly every day, or intermittently throughout a period of more than one year.
• Etiology not related to the use of medications or other medical conditions.
Tics can be motor or vocal, simple or complex. Simple motor tics usually affect only one muscle and can be rep- resented by eye blinking, eye movement, nose twitching, shoulder shrugging, mouth opening, and so on. Complex motor tics can include more complex movement, often in sequence, such as jumping, twisting, spitting, touching, smelling, rubbing, and copropraxia (obscene gestures).
Simple vocal tics are represented by various noises or sounds, such as throat clearing, snorting, sniffing, cough- ing, or barking. Complex vocal tics include words, phrases, echolalia, and coprolalia (obscene words or phrases). Patients describe an “involuntary urge” like tin- gling or itching to perform the movement or make the sound. The Tourette’s syndrome classification study group has defined these feelings as sensory tics: uncom- fortable sensations that can be focal, localized, or gen- eralized, and are relieved by the movement of the affected body part.
TS usually manifests in the first decade of life and has a male predominance. Motor and vocal tics are precipi- tated by stress, fatigue, and emotional excitement, and can be temporarily suppressed, for example, when the child is in school. Typically they increase when the child is relaxing, for example, when watching television. Tou- rette patients tend to have obsessive compulsive behav- iors in over half the cases. Other disorders associated with Tourette syndrome include attention deficit–hyperactivity disorder, mood disorder, depression, antisocial behavior, anxiety disorder, dyslexia, and so on. The long-term prog- nosis of TS is favorable with spontaneous remission or marked improvement of the symptoms in over half of the cases.
Other movement disorders need to be distinguished from tics and enter in the differential diagnosis of the patient in the vignette. Hyperkinetic movement disorders that need to be differentiated from tics include myo- clonus, dystonia, chorea, akathisia, tardive dyskinesia, stereotypes and psychogenic movement disorders.
Myoclonus is defined as a brief, sudden, shock-like movement caused by an abrupt contraction of a muscle
or a group of muscles. It can be focal, multifocal, seg- mental, or generalized, and can be physiological, e.g., associated with epilepsy or secondary to hypoxia or met- abolic, or toxic disorders.
Dystonia manifests with prolonged muscle contrac- tions causing repetitive movements or abnormal postures.
Dystonic tics, such as twisting, pulling, or squeezing, usually are preceded by an urge and are responsible for abnormal twisting or posturing that only last as long as the tic.
Chorea is characterized by involuntary, irregular, rapid, purposeless movements that cannot be suppressed but can be incorporated by the patient in a semipurposeful move- ment and is not preceded by an urge to make the movement.
Akathisia is definied as motor restlessness that cannot be suppressed and does not have an urge to make the movement, and varies in severity from jumpiness and fidgetiness to inability to sit or stand still.
Tardive dyskinesia, which typically occurs in patients treated with neuroleptics, includes a variety of involun- tary movements that can be choreoathetoid and dystonic, and preferentially involve the oral-buccal and lingual region.
Stereotypes are involuntary stereotyped movements, such as arm flapping and hand waving, that can occur during stress or excitement, and can decrease if the child is distracted.
Tics can be secondary to acute and chronic insult caus- ing cerebral dysfunction, such as trauma, cerebrovascular accident, encephalitis, and so on, or can be secondary to metabolic disorders such as hypoglycemia, toxic agents such as carbon monoxide, or drug ingestion such as neu- roleptics, lithium, levodopa, and so on.
Hereditary neurodegenerative disorders can also be associated with tics, in particular neuroacanthocytosis, Huntington’s disease, Hallervorden-Spatz disease, and so on.
Treatment
The medical treatment of tic disorder is particularly im- portant when tics affect the quality of life and create a disabling psychosocial situation.
Alpha agonist agents, such as clonidine and guanadine, are now the first line of treatment and may be particularly useful in children with hyperactivity. Neuroleptic drugs, such as pimozide, haloperidol, and fluphenazine, have been widely used for TS. Pimozide is less sedative than haloperidol but may cause prolonged QT interval. Halo- peridol can have several adverse effects, such as acute dystonic reactions, school phobia, depression, and par- kinsonism. Atypical neuroleptics (risperidone, olanza- pine, and ziprasidone) have fewer motor adverse effects and are also used. Botulinum toxin has been considered for patients with disabling intractable tics.
Alternative approaches include behavioral treatments such as relaxation techniques, biofeedback, and hypnosis.
References
Huntington’s Disease
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Tic Disorders
Erenberg, G. The clinical neurology of Tourette syndrome. CNS Spectrum 4:36–53, 1999.
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